Functionalization of sisal fibers and high‐density polyethylene by cold plasma treatment

Chopped sisal fibers and finely powdered high‐density polyethylene were surface functionalized using dichlorosilane (DS) under radio frequency (RF)‐plasma conditions and characterized by electron spectroscopy for chemical analysis (ESCA) and fluorescence labeling techniques. A high‐capacity (10 L), rotating, 13.56 MHz, electrodeless plasma installation, specially designed to allow the uniform surface modification of powdery and particulate matter of irregular shape, was used. A three‐factor fractional experimental design was employed to evaluate the effect of RF‐power, pressure, and reaction time on the ESCA‐based relative atomic composition of plasma‐treated samples. It was demonstrated that ? SiH_xCl_y functionalities are present on plasma‐exposed surfaces and these functionalization reactions can be controlled by selecting proper plasma parameters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2145–2154, 2002     

Ester and epoxide functionalization of high‐density polyethylene by thermolysis method—An FTIR study

High‐density polyethylene was functionalized using a thermolysis method in the presence of functionalized peroxides at different temperatures and at various peroxide concentrations. It was found that both percentage cross‐linking (% CL) and percentage functionalization (% Fn) increased with an increase in peroxide concentration. The ester and epoxide functionalization was confirmed by FTIR spectroscopy. Ester functionalization was further confirmed by saponification and acidolysis reaction. The functionalization capacities of acrylic ester peroxide and acrylic acid peroxide were determined and compared. A plausible reaction mechanism has been proposed to explain the experimental results obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 761–765, 2005     

Mechanical and thermal properties of high‐density polyethylene toughened with glass beads

Glass beads were used to improve the mechanical and thermal properties of high‐density polyethylene (HDPE). HDPE/glass‐bead blends were prepared in a Brabender‐like apparatus, and this was followed by press molding. Static tensile measurements showed that the modulus of the HDPE/glass‐bead blends increased considerably with increasing glass‐bead content, whereas the yield stress remained roughly unchanged at first and then decreased slowly with increasing glass‐bead content. Izod impact tests at room temperature revealed that the impact strength changed very slowly with increasing glass‐bead content up to a critical value; thereafter, it increased sharply with increasing glass‐bead content. That is, the Izod impact strength of the blends underwent a sharp transition with increasing glass‐bead content. It was calculated that the critical interparticle distance for the HDPE/glass‐bead blends at room temperature (25°C) was 2.5 μm. Scanning electron microscopy observations indicated that the high impact strength of the HDPE/glass‐bead blends resulted from the deformation of the HDPE matrix. Dynamic mechanical analyses and thermogravimetric measurements implied that the heat resistance and heat stability of the blends tended to increase considerably with increasing glass‐bead content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2102–2107, 2003     

Preparation of granular crosslinkable medium‐density polyethylene

Granular crosslinkable medium‐density polyethylene (XLPE) without scorch inhibitor was prepared adding organic peroxide [2, 5‐dimethyl‐ 2, 5‐ di‐ (t‐butyl‐peroxy) hexyne‐3] through extrution process, in industrial scale. Twin screw extruder was used to mix the polyethylene and the peroxide. The temperature zones of the extruder were controlled very carefully to prevent unwanted crosslinking during extrusion. Compression molding, rotational molding, and injection molding of XLPE at 155°C made no crosslinking in PE, and then they were exposed to higher temperatures at which the organic peroxide decomposed to provide free radicals which led to the crosslinking of the MDPE. The thermal properties (using dynamic mechanical analysis, DMA, differential scanning calorimetric analysis, DSC, and thermogravimetric analysis, TGA, techniques) and mechanical properties (including strain at break and stress at break) of virgin PE, crosslinkable PE, and crosslinked PE have been compared. The crossliked PE and virgin PE were also studied by X‐ray diffraction (XRD) technique. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1873–1879, 2007     

Surface characterization of polyethylene films modified by gaseous plasma

Of the several techniques available for surface modification, plasma processing has proved to be very appropriate. The low temperature plasma is a soft radiation source and it affects the material only over a few hundred angstroms deep, the bulk properties remaining unaffected. Plasma surface treatment also offers the advantage of greater chemical flexibility. The improvement in adhesion was studied by measuring T‐peel strength. In addition, printability of plasma‐treated PE films was studied by cross test method. It was found that printability increases considerably for plasma treatment of short duration. It was therefore thought of as interesting to study the surface composition and morphology by contact angle measurement, ESCA, and AFM. Surface energy and surface roughness can be directly correlated to the improvement in above‐mentioned surface‐related properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 449–457, 2007     

Mechanical and thermo‐physical properties of high‐density polyethylene modified with talc

The aim of this study was to examine the physical, mechanical, and thermo‐physical properties of high‐density polyethylene (HDPE) modified with talc. Different weight fractions of talc (up to 35 wt %) were compounded with an HDPE matrix containing 2.5 wt % of carbon black (CB) in a twin‐screw compounder. The composites were then processed by injection moulding to obtain specimens for testing. The results indicate that CB causes a significant decrease in the toughness, while talc not only enhances the thermal conductivity and thermo‐physical properties of the composites but can also play a role in compensating for the negative effects of CB on impact resistance. The experimental data show that the presence of CB reduces the impact resistance of HDPE by up to 34%, while addition of up to 8 wt % talc can return this value to close to that of pure HDPE. No significant effect on the composite tensile yield and fracture strength was observed for either component at all concentrations. The thermal conductivity, thermal diffusivity, and specific density values of the composites increased almost linearly, but the increase in moisture absorption in the long term showed nonlinear behavior in the concentration range of the experiment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crosslinking of high‐density polyethylene in the presence of organic peroxides

The crosslinking efficiency of various commercially available organic peroxides (dicumyl peroxide, O,O‐t‐butyl O‐2‐ethylhexylperoxycarbonate, t‐butyl peroxybenzoate, t‐butyl 3,5,5‐trimethylperoxyhexanoate, and t‐butyl 2‐ethylperoxyhexanoate) was tested on high‐density polyethylene (HDPE) in its molten state. The variations of the concentrations of the peroxides versus the crosslinking extent were plotted for these peroxides, and the values were compared. Dicumyl peroxide was found to be the best crosslinking agent for HDPE. The efficiency of the HDPE crosslinking with each peroxy derivative was analyzed on the basis of the behavior of the radicals generated from it. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 75–81, 2004     

Wood‐thermoplastic composites from wood flour and high‐density polyethylene

High‐density polyethylene/wood flour (HDPE/WF) composites were prepared by a twin‐screw extruder. The effects of WF, silane coupling agents, polymer compatibilizers, and their content on the comprehensive properties of the WF/HDPE composites have been studied in detail, including the mechanical, thermal, and rheological properties and microstructure. The results showed that both silane coupling agents and polymer compatibilizers could improve the interfacial adhesion between WF and HDPE, and further improve the properties of WF/HDPE composites, especially with AX8900 as a compatibilizer giving higher impact strength, and with HDPE‐g‐MAH as a compatibilizer giving the best tensile and flexural properties. The resultant composite has higher strength (tensile strength = 51.03 MPa) and better heat deflection temperature (63.1°C). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of recycled polypropylene on polypropylene/high‐density polyethylene blends

The effect of recycled PP on incompatible blends of virgin polypropylene (PP) and high‐density polyethylene (HDPE) was studied. Recycled PP from urban solid waste was extracted with methyl ethyl ketone and the compatibilizing action of the product before and after extraction was examined. The characterization of the recycled PP was performed by FTIR, NMR, and DSC analyses. Mechanical properties of the blends were evaluated. The results showed partial compatibility of the blend components, reflected in the improvement of the tensile strength and elongation. Best results were achieved by the addition of extracted recycled PP on the 50/50 PP/HDPE blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1305–1311, 2001     

Effect of silane grafting on the microstructure of high‐density polyethylene/organically modified montmorillonite nanocomposites

Organically modified montmorillonite (org‐MMT) and high‐density polyethylene (HDPE) grafted with silane groups (HDPE‐g‐silane) were melt compounded to give HDPE‐g‐silane‐blend‐org‐MMT nanocomposites. X‐ray diffractometry was performed to investigate the intercalation effect. Transmission electron microscopy was applied to observe the dispersion of org‐MMT layers in HDPE matrices. The results indicate that an intercalated structure can be easily obtained in HDPE‐g‐silane‐blend‐org‐MMT nanocomposites. Furthermore, positron annihilation lifetime spectroscopy was used to characterize the microstructure of the composites. It is found that the ortho‐positron (o‐Ps) intensity for HDPE‐g‐silane is decreased by approximately 10% with a narrower lifetime distribution than that for HDPE. With increasing org‐MMT concentration, the o‐Ps intensity I₃ increases for HDPE‐g‐silane‐blend‐org‐MMT nanocomposites; however, for HDPE‐blend‐org‐MMT composites I₃ decreases. It is found that HDPE composites with good dispersion can be obtained following appropriate modification of the HDPE. And silane grafting has an effect on the free volume of the HDPE nanocomposites. Copyright © 2007 Society of Chemical Industry     

Anomalous heat capacity of high‐density polyethylene melts at high temperature

The first measurements of heat capacity of high‐density polyethylene have been obtained for melts in the high‐temperature region of 180–260°C. A heat‐flow twin calorimeter was used. Abrupt transitions are noticed at 212 and 228°C, analogous to transitions seen earlier with rheological and surface tension measurements. Possible explanations for these phenomena are offered. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dynamic rheological behavior of high‐density polyethylene filled with carbon black

The dynamic rheological behavior of high‐density polyethylene (HDPE) composites filled with carbon black (CB) was studied by controlling periodic small shear strains at constant temperatures. The results shed light on the relationship between the behavior of dispersed fillers and polymeric matrix systems. At sufficiently high filler concentration a structural skeleton seems to appear, which significantly raises the modulus at the low frequency region. High structure, finer size acetylene black raises the modulus significantly more than does the low structure and larger size one (e.g., N550). Oxidized CB increases the modulus in the whole frequency region for the enhanced interaction between polymer matrix and CBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3527–3531, 2002     

Properties of high‐density polyethylene filled with waste crosslinked foam

Crosslinked polyethylene foam is widely used in packaging and as an insulation material. Finely ground waste of such crosslinked foam mesh size 7 or particle size less than 2815 μm is used as a filler in high‐density polyethylene (HDPE) of two different grades (7.5 and 21 MFI). Mechanical, thermal, and morphological properties of filled composites is studied experimentally. Waste foam powder concentration was varied up to 40% by weight basis. Impact strength of base HDPE increased by a factor of six. The overall changes in mechanical properties are similar to the crosslinking effect. It is believed that waste foam particles act as a point of entanglement with different chains of polyethylene. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 110–114, 2004     

Glass‐transition‐temperature depression in chemically crosslinked low‐density polyethylene and high‐density polyethylene and their blends with ethylene vinyl acetate copolymer

A reduction in the glass‐transition temperature (T_g) was found for polyolefins chemically crosslinked by peroxide. This tendency, which was observed for low‐density and high‐density polyethylenes, was also validated for their blends with Ethylene Vinyl Acetate copolymer. It is proposed that the constrained crystallization process, as a result of a restriction imposed on the chain packing by the chemical crosslinks, results in an increasing net free volume in the amorphous phase and hence reduces T_g. The T_g depression becomes greater with increasing crosslink density, whereas at the same time, the degree of crystallinity and consequently the density of the system decreases with an increase in the peroxide content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1654–1660, 2007     

Oil‐absorption function of physical crosslinking in the high‐oil‐absorption resins

The concept of physical crosslinking was introduced into the research field of oil‐absorption resins, which were traditionally synthesized only by chemical crosslinking. Specifically, the partially physical crosslinking acrylic series for high‐oil‐absorption resins were prepared in the suspension process, and the swelling behavior of the samples was observed and recorded online. This demonstrated that a kind of relaxing three‐dimensional network was indeed formed by the introduction of polybutadiene (PB). The effects of monomer feed ratios, crosslinking agent concentration and type, particle size, and temperature on the oil absorbency and oil‐absorption speed were investigated. The results indicated that there were an optimum monomer feed ratio and an optimum amount of ethylene glycol dimethacrylate or PB. In addition, the particle size and temperature had a serious influence on the oil‐absorption speed in comparison with the monomer feed ratio and the crosslinking agent concentration and type. The results also showed that particle size affected oil absorbency to a great degree and that the effect of temperature on oil absorbency was complex. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3945–3950, 2003     

Successive solution fractionation mechanisms for high‐density polyethylene

BACKGROUND: Preparative fractionation techniques are currently used in order to obtain large amounts of polyethylene fractions. Preparative successive solution fractionation (SSF) and temperature rising elution fractionation (TREF) are compared as regards obtaining, at a multi‐gram scale, low‐dispersity fractions of high‐density polyethylene (HDPE). The operative separation mechanisms during a SSF of a broad HDPE, which are not yet totally elucidated, are also studied in this work. RESULTS: SSF and TREF approaches lead to the separation of HDPE macromolecules according to their molar masses. If very homogeneous fractions (dispersities from 1.1 to 1.3) are isolated in TREF at the lowest elution temperature, the collected mass is too low. At higher elution temperatures, the fractions have too broad a molar mass distribution (dispersities from 2.7 to 3.7). With the SSF procedure, dispersities are not as low as for the first TREF fractions. But, the relative weight fraction is better distributed between the different extraction temperatures. The molar mass distribution exhibits a dispersity of around 1.9. CONCLUSION: The SSF method is the most suitable way to obtain large gram amounts of low‐dispersity (ca 2) HDPE fractions over a wide molar mass range. Complementary gram‐scale rheological characterization is thus possible enabling a better comprehension of the SSF mechanism. Liquid–liquid demixing is the main mechanism in SSF, but its relative importance depends on polymer characteristics and solvent quality. Copyright © 2008 Society of Chemical Industry     

Preparation of high‐performance polyethylene via a novel processing method of combining dynamic vulcanization with a silane‐grafted water‐crosslinking technique

A novel processing method of combining dynamic vulcanization with the silane‐grafted water‐crosslinking technique to improve the comprehensive properties of polyethylene (PE) is reported. PE was grafted with vinyl triethoxysilane (VTEO) first, and then, N,N,N′,N′‐ tetragylcidyl‐4,4′‐diaminodiphenylmethane epoxy resin was dynamically cured in a PE‐g‐VTEO matrix through a twin‐screw extruder to prepare PE‐g‐VTEO/epoxy blends. Polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) was used as a compatibilizer to improve the interaction between PE‐g‐VTEO and the epoxy resin. The results show that the novel processing method improved the strength, stiffness, and toughness of the blends, especially the heat resistance of the blends, by the addition of the dynamically cured epoxy resin as the reinforcement. PE‐g‐MAH increased the compatibility between PE‐g‐VTEO and the epoxy resin, which played an important role in the improvement of the comprehensive properties of the blends. In addition, after treatments in both hot air and hot water, the comprehensive properties of blends were further improved, thanks to the further curing reaction of epoxy with PE‐g‐VTEO. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fine‐structure and physical properties of polyethylene fibers in high‐speed spinning. I. Effect of melt‐flow rate in the high‐density polyethylene

High‐density polyethylene (HDPE) fibers, obtained from a melt‐flow rate (g/10 min) of 11 and 28, was produced by a high‐speed melt‐spinning method in the range of take‐up velocity from 1 to 8 km/min and from 1 to 6 km/min, respectively. The change of fiber structure and physical properties with increasing take‐up velocity was investigated through birefringence, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph‐M. With an increase in take‐up velocity, the birefringence showed a sigmoidal increase, which has distinct changes in the range of 1–5 km/min. Throughout the whole take‐up velocities, the birefringence of HDPE(11) was higher than that of HDPE(28). With increasing take‐up velocity, the crystalline orientation was transformed from a‐axis orientation to c‐axis orientation. These crystalline relaxations are confirmed by the tan δ peak of high‐speed spun HDPE fibers. The intensity of the crystalline relaxation peak decreases with increasing take‐up velocity in both HDPE(11) and HDPE(28). As above, the crystalline relaxation peaks shift to lower temperature with increasing take‐up velocity. With increasing take‐up velocity, the ultimate strain decreases while both specific stress and the initial modulus increase. The mechanical behavior may be closely related to, as investigated by birefringence, orientation of the amorphous region, etc., the take‐up velocity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1182–1195, 2000     

Processability‐enhanced bimodal high‐density polyethylene with comb‐branched high‐density polyethylene

Two solution reactors in series were utilized to synthesize comb‐branched high‐density polyethylene (HDPE), cbHDPE, where the first reactor prepares vinyl‐terminated HDPE macromers catalyzed by an organometallic catalyst favoring beta hydride transfer and the second reactor copolymerizes HDPE macromers with ethylene using a different organometallic catalyst capable of incorporating macromers. A bimodal HDPE, biHDPE with bimodalities in molecular weight, and hexene content of the desired composition distribution was also prepared in a gas phase reactor using silica supported dual organometallic catalysts. By blending 3% solution‐made cbHDPE into the gas‐phase biHDPE, the resulting trimodal HDPE preserves the excellent stiffness and toughness of the bimodal HDPE while having exceptional melt strength and processability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45755.     

High‐density polyethylene modified by polydimethylsiloxane

High‐density polyethylene (HDPE) was modified by the grafting of polydimethylsiloxane (PDMS) through a free‐radical process, in a melt‐mixer chamber, using dicumyl peroxide (DCP) as an initiator. The influence of PDMS (0.2–0.8 mol %) and peroxide (0.03–0.08 mol %) concentrations on the grafting, final torque, and melt flow rate (MFR) of copolymers were investigated using factorial planning. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), MFR, and rheometry were used to characterize the copolymers obtained. Surface plots showed that higher degrees of grafted PDMS and higher final torques were obtained with increase in the PDMS amount at low DCP levels and with increase in the DCP amount at low PDMS levels. The peaks of fusion and crystallization of the copolymers showed no significant changes with respect to HDPE. Data of MFR and GPC suggested that crosslinking reactions and/or chain extension occurred concomitant with the grafting reactions. Copolymers with high grafting degrees showed high MFR and low dynamic shear viscosities in comparison with low grafting degree copolymers, which is probably due to the migration of the PDMS‐containing copolymers on the surface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3460–3467, 2001